Clearly one would sacrifice as high a price as was required for the particular favour being asked of the god in question.
The minor, personal, types of sacrifice were more properly referred to as Victima or Hostia whilst the word “Sacrificium” was generally referred to the “victim” of the more important public ceremonies.
Public sacrificial ceremonies were state affairs which would generally take place in the Forum according to strict liturgy and hymns called “carmina“. The value of the sacrifice would be in proportion to the State’s needs. We can imagine whole herds of cattle being religiously gored at the sacrificial altar. Various cuts of the meat would be reserved for the gods whilst the rest would be eaten in one huge religious feast.
Clearly, each deity had his or her own specific rites to be followed in the sacrificial ceremony but there were also a number of common elements.
The procession would be preceded by a public crier who shouting “hoc age” would lead the public to stop working and attend the ritual. Musicians would assist the crier either by playing their instruments or doing a little shouting themselves.
The procession proper was headed by the chief priest and possibly the individual offering/funding the actual sacrifice(s). These persons would be dressed in the purest white.
The animal to be sacrificed would also be dressed up for the occasion. Normally this might include some gold on the horns (if it had any), a frilly collar and a crown of leaves taken from the plant or tree most sacred to the divinity in question.
Once they had arrived to the altar the actual sacrifice would commence. An officer of the procession would shout “Favete Linguis” to entice all attendants to keep silent. A piper would start to play and continue throughout the ceremony in order to drown out any unwanted and potentially negative noise.
At this point the Priest would touch the altar with one hand and deliver a prayer to the god(s) in question. This prayer would always start with mention of the god Janus and finish with the goddess Vesta, suggesting that these two divinities were generally regarded as a good bracket within which to summon all the others.
The ceremonial killing of the beast, or Immolatio, would follow. This included sprinkling some cereal and scents mixed with salt over the animal. Then the priest would take a sip of wine from a cup which he would then offer to those about him. This was called Libatio and is obviously very reminiscent of the later Christian communion.
The last of the wine would be poured between the sacrificial animal’s horns. Some hairs would be taken from the same area and cast into the sacred fire, this would be a sort of “hors d’oeuvres” for the gods I suppose. Then turning to the East or South East (towards the Alban hills I think) the priest would trace a line from head to tail on the animal and hand it over to his aids called “Victimarii” for it to be killed.
The animal was killed, skinned, opened up and washed so that the Aruspices could move in, take a good look and make their predictions. The animal would then be butchered and those parts which weren’t reserved for the gods would be cooked and consumed by those attending the ceremony.
A law was passed in the first century BC forbidding human sacrifices, which suggests that before then these were not unheard of. Having said that, we shouldn’t forget the sacrificial fights inherited from the Etruscans and which later grew to be the Gladiatorial fights. These were generally known as “munere“, meaning “offerings” and their origins lay in the sacrificial fight to the death of slaves and captives in honour of the deceased person at his funeral.